1. Field of the Invention
The present invention relates to an image generation by using a computer, that is, a field of computer graphics, more particularly to superposing a plurality of images each of which changes its brightness.
2. Description of the Related Art
An image generation technology by using a computer is utilized in various ways, for example, in a field of computer games. In the field of computer games, for example, in the hardware constitution shown in FIG. 1, a variety of images are generated and a plurality of the generated images are synthesized.
In FIG. 1, a CPU 102 controls the processing of the entire system. An input interface 104 performs interfacing to enter an input from an input apparatus (not shown) to the system. A sound device 106 generates music and effect sound by control of the CPU 102, and outputs them through speaker (not shown). A ROM 108 and a RAM 110 store programs and data used by the CPU 102, a geometry processing device 112 and the like.
The CPU 102, for example, stores such as geometry data corresponding to a location information of a car which is operated by a game player, in a geometry memory 114. The geometry processing device 112 reads out geometry data stored in the geometry data memory 114, and performs a three-dimensional coordinate transformation processing on data of a vertex data memory 120. Based on the three-dimensional data which performed the coordinate transformation processing, the geometry processing device performs an image generation processing in order for a drawing device 116 to display an image by referring to data of a texture memory 122 if necessary. The result is stored in a frame memory 118. Then, the geometry-processing device 112 reads out image data displayed from the frame memory 118, and sends the data to a display apparatus (not shown), thus displaying a game.
In an image generation and synthesis by using the above-described constitution for a game, there are cases where a plurality of images each of which changes its brightness as shown in FIG. 2(a) are superposed and synthesized. Such processing is often performed in the drawing device 116 in FIG. 1. FIG. 2(b) shows the change of brightness of a half of an image in the case that the brightness is symmetric with respect to a point. On the graph in FIG. 2(b) showing a relation between the position and the brightness of the image, there is a point where primary differential of its brightness change is discontinuous. In the graph of FIG. 2(b), a point where a straight line is broken is the discontinuous point.
As described above, a synthesis by superposing of two images that change their brightness is considered. FIG. 3 shows the synthesis result. As shown in FIG. 3(a), when two images each of which changes its brightness are synthesized by superposing, a line called a xe2x80x9cmach bandxe2x80x9d may occur which is not intended to be made. The mach band will be described in a drawing shown in FIG. 3(b), which shows a relation between brightness and position when the two images are synthesized. FIG. 3(b) is a graph showing brightness change in the position of the x-axis direction shown in FIG. 3(a). The graph clarifies that the brightness of the image shows xcex1 and xcex2 at a point A and a point B respectively, where the two images synthesized are crossed, and that the brightness of the image changes such that the line is broken at the A and B points. At these A and B points primary differential becomes discontinuous, and thus the mach band occurs.
The object of the present invention is to prevent a mach band from occurring when two images each of that changes its brightness are synthesized by superposing.
In order to achieve the above-described object, the method of image synthesis of the present invention generates an image such that primary differential of its brightness is continuous, and performs an image synthesis without occurrence of mach band by superposing the plurality of the generated images.
Image processing may be performed so that a plurality of images are processed so as to make primary differential of brightness of each image continuous, and the processed images are superposed upon one another so as not to create mach band.
As described above, since image processing may be performed so that primary differential of brightness of an image to be synthesized is continuous, superposed images show continuous primary differential of brightness, and image brightness does not make an acute change. Accordingly, mach band does not occur.
An apparatus for realizing the above-described image synthesis method and a recording medium for storing a program which allows a computer to realize the image synthesis are also within the scope of the present invention.